High Light Acclimation Mechanisms Deficient in a PsbS-Knockout Arabidopsis Mutant.

Young Nam Yang,Thi Thuy Linh Le,Dong-Hee Lee,Ji-Hye Hwang,Eun-Ha Kim,Choon-Hwan Lee,Ismayil S. Zulfugarov,Jong-Seong Jeon,Hyun Uk Kim

doi:10.3390/ijms23052695

Abstract

The photosystem II PsbS protein of thylakoid membranes is responsible for regulating the energy-dependent, non-photochemical quenching of excess chlorophyll excited states as a short-term mechanism for protection against high light (HL) stress. However, the role of PsbS protein in long-term HL acclimation processes remains poorly understood. Here we investigate the role of PsbS protein during long-term HL acclimation processes in wild-type (WT) and npq4-1 mutants of Arabidopsis which lack the PsbS protein. During long-term HL illumination, photosystem II photochemical efficiency initially dropped, followed by a recovery of electron transport and photochemical quenching (qL) in WT, but not in npq4-1 mutants. In addition, we observed a reduction in light-harvesting antenna size during HL treatment that ceased after HL treatment in WT, but not in npq4-1 mutants. When plants were adapted to HL, more reactive oxygen species (ROS) were accumulated in npq4-1 mutants compared to WT. Gene expression studies indicated that npq4-1 mutants failed to express genes involved in plastoquinone biosynthesis. These results suggest that the PsbS protein regulates recovery processes such as electron transport and qL during long-term HL acclimation by maintaining plastoquinone biosynthetic gene expression and enhancing ROS homeostasis.

Highlights

IntroductionPlants have developed sophisticated acclimation mechanisms to cope with unpredictable challenges in their environment
Being sessile organisms, plants have developed sophisticated acclimation mechanisms to cope with unpredictable challenges in their environment
To monitor the changes in PSII photochemical efficiency (Fv/Fm) of plant leaves under high light (HL) illumination, leaves of Arabidopsis WT and npq4-1 mutants grown at low (70 μmol photons m−2 s−1) photosynthetic photon flux density (PPFD) and were harvested in the middle of the day followed by exposure to HL at 700 μmol photons m−2 s−1 for up to five days

Summary

Introduction

Plants have developed sophisticated acclimation mechanisms to cope with unpredictable challenges in their environment. When plants are exposed to excessive HL, the over-excitation of the photosynthetic apparatus triggers short-term protection mechanisms as well as several long-term acclimation processes. As an important short-term HL protection mechanism, non-photochemical quenching (NPQ) dissipates excess excitation energy as heat to reduce oxidative damage [1,2]. HL stress causes the generation of multiple reactive oxygen species (ROS), including hydrogen peroxide (H2O2), superoxide anion radicals (hereafter superoxide) (O2−), and singlet oxygen (1O2) that can cause damage and act as signaling molecules involved in regulating development and pathogen defense responses [9] The long-term protection mechanisms to HL stress or HL acclimation processes include dynamic changes in gene expression involved in hormone biosynthesis, signaling, and photosynthesis, the anthocyanin biosynthesis pathway genes [10], the composition, and the structure of the thylakoid membrane [11–14], accumulation of antioxidant metabolites and scavenging enzymes [15,16], and reducing LHCII antenna size [17–19]

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Discussion

Conclusion